[Anoncreds] Update "legacy" proof request to use W3C format anoncreds credentials

[ianco]

Update the "legacy" proof request to search W3C format credentials. These will need to be converted (on-the-fly I guess) to legacy format to include in the proof. This will require using the VCHolder to search for the credentials.

See for example: https://github.com/ianco/aries-cloudagent-python/commit/bfa0ac35a981d8d203d1710fa22dd6560bf75936